Sorption cycles involve the process of physical adsorption and the manipulation of a fluid through a medium which has a selective affinity for a component species or specie of the fluid. As a multi-component fluid passes through the medium, the species or specie is "adsorbed", and the fluid exiting the medium contains a predetermined species in a quantity less than that in the fluid originally entering, or conversely, the fluid exiting is relatively enriched in proportion to the components of the fluids which are not absorbed. Certain media are capable of "desorbing" the specie after adsorption (such as when they are heated or subjected to a "purge"); and an adsorption/desorption "cycle" is well known.
Sorption technology is of practical use in many applications of gas separation or purification. In these instances, given a particular commercial application, a cycle and corresponding apparatus is devised to accomplish a given task. The apparatus generally consists of one or more "beds" containing the sorbent medium, which is selected because of its affinity for a particular specie and a multiplicity of valves, pumps, connectors, regulators and other mechanical devices are interconnected to each other and to the bed(s) to permit repeated adsorption/desorption in a cycle to achieve an operating result consistent with the intended application.
In medical applications, pressure swing adsorption cycles have been found to be useful in oxygen concentration systems which provide a source of purified oxygen from an ambient air supply to a single, individual patient. Such oxygen concentration systems are used in the treatment of chronic obstructive pulmonary diseases (COPD) as a result of advances in the medical field which suggest that 24-hour continuous oxygen therapy is a perferred treatment of diseases which include chronic bronchitis, emphysema and asthma.
In contrast with therapeutic supplies of liquid or bottled oxygen, an oxygen concentration unit using an adsorption cycle provides advantages in portability and continuous operation. Several oxygen concentration units are now commercially available and generally provide flow rates of oxygen of from about 2 to 5 liters per minute at purity levels, depending on the rate of demand of from 95% at low demand to 80% at high demand. Disadvantages in such units are that in general a high, consistent purity of oxygen cannot be delivered at a high output rate, even despite the generally "low" volume oxygen production requirements imposed on the system. Here, the currently available oxygen concentration units are generally unable to meet the reasonably anticipated 5 liter per minute flow rate of delivery of a pure oxygen (95%) which may constitute the therapeutic demand required by an individual patient. In addition, even though such units are advantageous over supplies of liquid or bottled oxygen, the bulk and weight of the adsorption unit is considerable. Thus there exists a need for an improved oxygen concentration system, adaptable for medical treatment applications and which meets the stringent demands of reliability, compactness and consistent supply of high purity oxygen in a level which is consistent with the anticipated physiological need of an individual patient.